The display of images on large screens, particularly curved screens, is today used in many areas with varying degrees of success. One of the problems with using several video projectors in order to create a large image is that differences arise in the boundary areas of the images of the respective projectors.
Among other things, large screen displays are used in simulators, e.g. for driving practice or within the entertainment industry. Lately, the prices of such systems have been greatly reduced, especially for the simulator system, which runs underlying physical models upon simulation, as well as instructor and/or student user interfaces. This cost reduction has been brought about as a result of the recent developments in PC technology.
Lately, the use of real-time 3-dimensional graphics in the entertainment industry has resulted in a greater volume of sales for such systems, which again has resulted in a great reduction in the price of image generators, in the order of from hundreds of thousands of dollars to a couple of thousand dollars.
This price reduction has made possible the purchase of more simulators, in order to allow a greater number of persons to undertake simulator training in areas where simulator training has been extensively used, such as in the military and aviation in general.
Thus, up until now, the greatest cost associated with simulators has been the projection system. New production technology results in cheaper projectors, however these are not of a type that can automatically be used in simulators.
In this connection, it should be noted that the projection scene for a simulator is typically constructed as front projection systems using one or more projectors (in some cases more than 10) to create a panorama image. In order to achieve a panorama image, it is necessary to project the image onto a curved screen by using several projectors arranged side by side and/or possibly on top of each other. The above cheap projectors are designed to display a single image on a flat screen, and are therefore not automatically suitable for display on a curved screen.
The effect of overlapping zones between the various projection images is critical for certain simulator applications, it being necessary to ensure a seamless transition from one image (channel) to an adjacent image. When viewing a multi-projector image, it is also important to control the color and intensity between the projectors in order to be able to compensate for varying intensities in the image.
A further problem may be the fact that the standard lens of the above projector is designed for display on a flat screen. Thus there will be a limit to how curved the screen may be before the loss of optical focus presents a problem.
The known and expensive technology makes use of CRT (cathode ray tube) projectors, which are expensive to purchase and which require constant re-calibration. This re-calibration takes place so often that it is necessary to have extra personnel present during the use of the simulator to perform frequent calibrations, which also makes the running of the simulator more expensive. One advantage of this known technology is the fact that there is no fixed pixel raster for CRT, i.e. the geometry may be compensated for within reason.
The new projector technology includes LCD (Liquid Crystal Display) and DMD (Digital Micromirror Device), which differ from conventional CRT (Catode Ray Tube) based projectors in that they are cheaper to buy and have a fixed pixel raster. The advantage of the fixed pixel raster is that it does not drift, thus making continuous realignment, as in the case of the CRT, unnecessary. One disadvantage however, is that the fixed pixel raster makes it impossible to compensate for the curved screen geometry. When using several CRT projectors, the images are easily distorted in order for them to appear seemingly correct on a curved screen.
None of the technologies mentioned have a built-in capability for giving a soft transition from one image to the next.
An ideal projector would compensate for all of the above effects. The main requirement however, would be to be able to generate the necessary geometry distortion, to be able to modulate the intensity (digital color modulation) for generating soft transitions from one image to the next, and compensate for a varying intensity across the image field. One of the aims of the present invention is to provide the above.
In order to avoid operational problems connected with analogue electronics, the correction must be performed digitally. This means that the correction must be carried out at a point where pixel data is available in a digital form, i.e. either in the field oscillator or in the actual projector.
The above is effected by a correction module as described herein. The correction module according to the invention may be installed as a plug-in module in existing projectors. The only requirement that must be fulfilled is that digital pixel data is available in real-time, so that the data stream may be retrieved and re-formatted by the correction module. Physically, the correction module can be designed as a PCB-board to be mounted on top of an existing printed circuit board in the projector.
The invention may, in addition to being used for projectors in a simulator, also be used in the entertainment business and similar, with one of several possible applications being described in greater detail in the following.
A simulator projection theatre may be seen as a special case of a video wall, i.e. a multi-projector system used in a simulator. Analyses have shown that the construction of a high quality video wall requires approximately the same functions as for application in a simulator, the main difference being that a simulator requires a curved screen.
Important features of a video wall are that it is simple to erect and install, and that there are no analogue operational problems. A soft transition from one image to the next, combined with removal of hot spots, will result in a large, high quality image, as the seams between the projections may be made virtually invisible.
The geometry correction will accelerate the setting up of the projector system, because the requirement for exact mechanical alignment has been reduced. Digital keystone correction allows great freedom with respect to the choice of projector/screen within the limits of optical focus.
Setting up the video wall, including the geometry alignment, is made simpler by use of simple control, e.g. via a PC, laptop, that addresses all or individual projectors. This will also allow configuration data to be backed up on a disk.
Typical video wall applications require complex video splitters for an accurate deduction of individual frames from the source signal. One advantage of the geometry correction circuit is that it can be used to deduct frames directly from the source signal, thus avoiding the need for an external splitter. Instead, a simple video buffer system or a chained structure is used to distribute the source signal to all of the projectors.
The system setting will set up all the projectors to derive their relevant frames including an overlap zone for blending.